Within the art of fenestration products, such as windows and doors, it is well known that double panes of glass in a window provide better insulation than a single pane of glass. The provision of venetian type blinds or pleated shades between two panes of glass in a fenestration product is also known in the art to provide desired window or door coverage. A pleated blind between window panes is disclosed in the U.S. Pat. No. 4,913,213 to Schnelker. A venetian or slat blind between panes of glass is disclosed in the U.S. Pat. Nos. 4,687,040; 4,664,169 and 5,379,825. In order to utilize such blinds or shades effectively with the increased insulation of the double glass product, control mechanisms for lifting, lowering and tilting the blind or shade from one side of the window must be provided while maintaining the window seal. The art has provided cords and cables, sometimes driven by a motor or gear system, as the control mechanism. The most popular systems route the cord through an aperture drilled through the interior pane of glass.
U.S. Pat. No. 4,687,040 to Ball discloses a device for adjusting the tilt angle of slats of a slat blind positioned between the panes of glass. The device includes a hole in one pane of glass and a flexible cable passing through the hole. The cable is connected to a rectangular member which controls the rotation of the slats. When the cable is turned by external torque, the slats are tilted.
U.S. Pat. No. 4,913,213 discloses a pleated blind between double window panes and blind control means for raising and lowering the blind. One embodiment is comprised of an aperture in one pane of glass and a bolt with a center hole mounted in the aperture. An actuator cord passes through the bolt hole and further up and over a screen, if desired, thereby providing an external control mechanism.
U.S. Pat. No. 5,379,825 discloses a window blind between double panes of glass. One embodiment uses a lift cord and a control cord routed through a hollow screw passing through one of the panes of glass to provide external control of the blind.
The prior art has also developed more complicated control mechanisms that utilize cables and gear systems that pass through the window frame rather that the glass. U.S. Pat. No. 4,664,169 to Osaka et al. discloses a device for tilting slats of a venetian blind between double panes of glass. The device uses electrical power driving means to move a piezoelectric bimorph device in a horizontal plane. The piezoelectric bimorph device is mounted to a block having a threaded bore. The piezoelectric bimorph device mechanically moves an elongated V-shaped beam under two cross arms which control the rotation of the slats. When the beam is moved, the cross arms are tilted, thereby rotating the slats.
The complicated systems that require control mechanisms to be mounted in or routed through the window frame are relatively expensive to manufacture. Furthermore, in many of these systems gears and motors wear and then slip or fail. Many of these control devices require a head rail which is too wide to fit between the panes of those windows whose panes are not more than ¾ inches apart. Hence, these systems have never achieved the popularity of through the glass systems.
The problems of the prior art systems discussed above are not present if the control mechanism is a cord or cords routed between the edge of the interior glass panel and the window frame. In U.S. Pat. No. 4,913,213, Schnelker describes a pleated blind between window panes. In one preferred embodiment, the actuator cord is routed over the glass housing and any screen housing provided. An L-shaped guide having a single vertical and horizontal channel cut therein is fitted over the top edge of the glass housing. An actuator cord passes through the channel. A major problem with this system is that one cannot maintain a seal between the window frame and the edge of the glass housing. Another problem is that most blinds have four control cords, two lift cords and two tilt cords. If all four cords are routed through a single channel they tend to bind and interfere with one another.
In U.S. Pat. Nos. 5,611,381, 6,006,813 and 6,070,638, Jelic describes a window having a blind between two panes of glass. A cord guide is provided at the top edge of the housing, with the cord guide including multiple slots for the lift and tilt cords. The cord guide maintains a seal between the window frame and the window panes and keeps the cords separated. However, in this window system, the blind is still controlled by multiple cords routed around the window panes, which still tend to present problems for the user.
Even when the cord routing has been improved, between the glass window covering product may still have problems, such as jamming, when the lift cords experience slack during operation. These problems may occur when the lift mechanism is used too briskly or quickly, or when the window covering encounters some type of obstruction. With the blind located between two glass panels, resolution of a jam in the lift cord is not an easy matter. Therefore, lift cord systems and blind actuation mechanisms that reduce the risk of slack and jamming are preferred.